Image processing device and image display device

ABSTRACT

An image processing device for converting a color tone of an image includes: an input unit to which an image is input; a designation unit that designates precision of color conversion performed on the input image; a color conversion table that stores output color data after color conversion of color data, which is determined according to the designated precision and may be included in the image, in an address space determined according to the precision; an address specifying unit that specifies an address referring to the color conversion table on the basis of a first portion, which is determined according to the precision, of color data expressing the input image; a color converting unit that converts the color data included in the input image into output color data by referring to the specified address of the color conversion table; a parameter specifying unit that specifies a parameter for interpolating a color, which is expressed by the output color data, on the basis of a second portion other than the first portion of the color data included in the input image; and an interpolation unit that interpolates a color, which is expressed by the converted output color data, on the basis of the specified parameter.

This is a Division of application Ser. No. 12/035,665 filed Feb. 22,2008. The disclosure of the prior application is hereby incorporated byreference herein in its entirety.

The entire disclosure of Japanese Patent Application No. 2007-043708,filed Feb. 23, 2007 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a technique of converting a color toneof an image.

2. Related Art

In recent years, many image display devices, such as CRT displays,liquid crystal displays, plasma displays, and projectors, have aplurality of output modes of an image that is displayed. Such modesinclude a dynamic mode in which brightness or saturation is emphasized,a cinema mode in which correction to a color tone suitable for watchinga movie is made, and the like.

As a technique of performing color conversion according to an outputmode, there is a technique of using a three-dimensional lookup table(hereinafter, referred to as “3D-LUT”) (refer to JP-B-58-16180). Therelationship of correspondence between an input color and an outputcolor is recorded in the 3D-LUT. An image display device stores the3D-LUT in a memory and converts a color tone by referring to the stored3D-LUT. The image display device can meet various kinds of modes byproperly rewriting the 3D-LUT stored in the memory according to anoutput mode.

In the 3D-LUT, the data volume is increased if color conversion isperformed with high precision. As a result, the size of a circuit forperforming color conversion is increased. For this reason, the circuitfor performing color conversion was redesigned, in many cases, for everymodel according to the purpose of use and price range of an imagedisplay device. However, as an integration degree of an LSI increases inrecent years, it has become possible to share a color conversion circuitwith relatively low cost even if a circuit is not designed for everymodel. However, among image display devices, there is an image displaydevice, such as a low-cost projector used for presentation, which doesnot require such precision of color conversion. Accordingly, in the caseof sharing a circuit on the basis of the specification of a high-classmodel, there was a case in which the excessive quality was obtaineddepending on a model of an image display device. In addition, if thedata volume of the 3D-LUT is increased, it takes time to load the datato a memory. As a result, depending on a model or application of animage display device, there was a possibility that an adverse effectwould be noticeable, for example, it would take time to performswitching of an output mode although such precision of color conversionwas not necessary.

SUMMARY

An advantage of some aspects of the invention is that it provides adevice capable of meeting color conversion with various kinds ofprecision.

According to an aspect of the invention, an image processing device forconverting a color tone of an image includes: an input unit to which animage is input; a designation unit that designates precision of colorconversion performed on the input image; a color conversion table thatstores output color data after color conversion of color data, which isdetermined according to the designated precision and may be included inthe image, in an address space determined according to the precision; anaddress specifying unit that specifies an address referring to the colorconversion table on the basis of a first portion, which is determinedaccording to the precision, of color data expressing the input image; acolor converting unit that converts the color data included in the inputimage into output color data by referring to the specified address ofthe color conversion table; a parameter specifying unit that specifies aparameter for interpolating a color, which is expressed by the outputcolor data, on the basis of a second portion other than the firstportion of the color data included in the input image; and aninterpolation unit that interpolates a color, which is expressed by theconverted output color data, on the basis of the specified parameter.

In the image processing device according to the aspect of the invention,a color conversion table used for color conversion, an address thatrefers to the color conversion table at the time of color conversion,and a parameter for interpolating a color after color conversion aredetermined according to the precision of color conversion designated bythe specifying unit. Accordingly, it is possible to provide a devicecapable of meeting color conversion with various kinds of precision. Inaddition, not only the entire portion excluding the first portion butalso a predetermined portion of a portion excluding the first portionmay be included in a range of the second portion other than the firstportion.

In the image processing device having the configuration described above,the size of the address space of the color conversion table may bedetermined on the basis of a value obtained by multiplying the number ofsteps of a color depth of the output color data, which is determinedaccording to the designated precision, three times. According to theimage processing device having the configuration described above, thesize of the color conversion table can be specified according to theprecision designated by the specifying unit.

Furthermore, in the image processing device having the configurationdescribed above, the address specifying unit may specify the address bydividing color data included in the input image into high-order bit dataand low-order bit data on a boundary determined according to the colordepth and treating the high-order bit data as the first portion.According to such a configuration, color data included in image data canbe divided into data used to specify an address and the other dataaccording to the precision designated by the specifying unit.

Furthermore, in the above configuration, the color depth (=D) and thebit number (=U) of the high-order bit data may satisfy the followingrelationship of D=2^U or D=2^U+1 (where “^” is a symbol indicating thepower).

Furthermore, in the image processing device having the configurationdescribed above, the parameter specifying unit may treat the low-orderbit data as the second portion. In such a configuration, a part of colordata included in image data can be used as a parameter for interpolatingthe output color data after color conversion. Specifically, assumingthat the bit number of the low-order bit data is “L”, the interpolationunit interpolates the output color data, of which a color depth isreduced by the color converting unit, by an interpolation operationdetermined on the basis of which position a coordinate indicated by thelow-order bit data exists within a cubic region where a length of oneside is E(=2^L).

In addition, the invention may also be configured as, for example, animage display device or a projector, a method of outputting an image byusing an image processing device, and a computer program for changing acolor tone of an output image in addition to the configuration as theimage processing device described above. Such a computer program may berecorded in a computer-readable recording medium. Various kinds ofmediums, such as a flexible disk, a CD-ROM, a DVD-ROM, a magneto-opticdisk, a memory card, and a hard disk, may be used as the recordingmediums, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an explanatory view illustrating the schematic configurationof a projector.

FIG. 2 is a block diagram illustrating the specific configuration of animage processing circuit.

FIG. 3 is an explanatory view schematically illustrating an addressspace of an LUT memory.

FIG. 4 is an explanatory view illustrating a method of calculating anaddress when a cinema mode is set.

FIG. 5 is an explanatory view illustrating a method of calculating anaddress when a television mode is set.

FIG. 6 is an explanatory view illustrating a method of calculating anaddress when a presentation mode is set.

FIG. 7 is an explanatory view illustrating types of six tetrahedronsincluded in one cubic region.

FIG. 8 is an explanatory view conceptually illustrating how atetrahedron is selected by an address operation circuit.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, in order to clarify operations and effects of theinvention, an explanation will be made in the following order on thebasis of embodiments of the invention.

A. Configuration of projector

B. Configuration of image processing circuit

C. Modifications

A. CONFIGURATION OF PROJECTOR

FIG. 1 is an explanatory view schematically illustrating theconfiguration of a projector 100 according to an embodiment of theinvention. As shown in the drawing, the projector 100 according to theembodiment includes an input interface 170, an image processing circuit110, a liquid crystal panel driving circuit 130, a liquid crystal panel140, a light source portion 150, a projection lens 160, and an operationpanel 180.

An external device that outputs an image signal is connected to theinput interface 170. The input interface 170 includes a circuit thatperforms A/D conversion of an analog image signal input from theexternal device and generates a digital signal having 8-bit data, thatis, 256-step data corresponding to each color of R (red), G (green), andB (blue). An external device connected to the input interface 170includes a DVD player, a video cassette recorder, and a personalcomputer, for example.

The image processing circuit 110 is input with a digital signal outputfrom the input interface 170 and converts a color tone of an imageexpressed by the digital signal. The projector 100 includes a pluralityof image output modes that are preset, and the image processing circuit110 converts the color tone of an image according to the image outputmodes. In the present embodiment, a “cinema mode” in which conversioninto a color tone suitable for watching a movie is performed, a“television mode” suitable for watching a television program, and a“presentation mode” suitable for making a presentation are assumed asimage output modes.

In the cinema mode, the image processing circuit 110 performs highlyprecise color conversion using a 3D-LUT having a 17-step color depth. Inaddition, in the television mode, the image processing circuit 110performs color conversion with intermediate precision using a 3D-LUThaving a 9-step color depth. In addition, in the presentation mode, theimage processing circuit 110 performs color conversion with lowprecision using a 3D-LUT having a 5-step color depth. That is, in thepresent embodiment, the precision of color conversion performed on aninput image varies according to an image output mode.

The operation panel 180 includes an operation button used when a usersets an image output mode. The operation panel 180 is connected to theimage processing circuit 110. The image processing circuit 110 changesan output mode of an image according to an operation signal input fromthe operation panel 180.

To the liquid crystal panel driving circuit 130, an image after colortone conversion, which is output from the image processing circuit 110,is input as a digital signal. Then, the liquid crystal panel drivingcircuit 130 drives the liquid crystal panel 140 according to the digitalsignal.

The liquid crystal panel 140 is a transmissive light valve that iscontrolled by the liquid crystal panel driving circuit 130 and thatforms an image using a liquid crystal element. When light emitted fromthe light source portion 150 is incident on the liquid crystal panel140, the liquid crystal panel 140 modulates the light and emits thelight to a side of a screen 200.

The light source portion 150 is a light source that emits light towardthe liquid crystal panel 140. The light source portion 150 includes alamp 151, from which light is emitted, and a lens 152, which emits thelight generated in the lamp toward a liquid crystal panel, as maincomponents.

The projection lens 160 is a lens that projects modulated light, whichis emitted from the liquid crystal panel 140, toward the screen 200 sidein an enlarged manner.

In the projector 100 having the configuration described above, it ispossible to convert the color tone of an image, which is input by theinput interface 170, using the image processing circuit 110 and toproject the image whose color tone is converted on the screen 200.

B. CONFIGURATION OF IMAGE PROCESSING CIRCUIT

FIG. 2 is a block diagram illustrating the specific configuration of theimage processing circuit 110 shown in FIG. 1. As shown in the drawing,the image processing circuit 110 includes an address operation circuit12, an LUT memory 14, an interpolation operation circuit 16, and acontrol unit 40. The address operation circuit 12 corresponds to an“address specifying portion” a “color converting portion”, and a“parameter specifying portion”, and the LUT memory 14 corresponds to a“color conversion table” and a “color converting portion”. In addition,the interpolation operation circuit 16 corresponds to an “interpolationportion”.

The control unit 40 is a unit that performs an overall control of theprojector 100. The control unit 40 includes a CPU, a ROM, and a RAM. TheCPU controls the projector 100 by loading a control program stored inthe ROM to the RAM and executing the control program.

In addition, 3D-LUT data prepared beforehand for every image output modeis stored in a non-volatile state in the ROM. When the control unit 40receives setting of an image output mode from a user through theoperation panel 180, the control unit 40 read the 3D-LUT datacorresponding to the mode from the ROM and writes the 3D-LUT data in theLUT memory 14. Thus, the image processing circuit 110 can perform colorconversion on the basis of the 3D-LUT data stored in the LUT memory 14.

The control unit 40 outputs a mode signal, which indicates a state of animage output mode set by a user, to the address operation circuit 12 andthe interpolation operation circuit 16. The address operation circuit 12and the interpolation operation circuit 16 perform operation andinterpolation processing on an address on the basis of the mode signal.

The LUT memory 14 is a memory circuit in which the 3D-LUT is stored. The3D-LUT is configured such that RGB data after color conversion, which isexpressed with a D-step color depth, corresponds to “D×D×D” addresses.For example, in a 3D-LUT corresponding to the cinema mode, RGB dataafter color conversion corresponds to 4913 (=17×17×17) addresses.Furthermore, in a 3D-LUT corresponding to the television mode, RGB dataafter color conversion corresponds to 729 (=9×9×9) addresses.Furthermore, in a 3D-LUT corresponding to the presentation mode, RGBdata after color conversion corresponds to 125 (=5×5×5) addresses.

FIG. 3 is an explanatory view schematically illustrating an addressspace of the LUT memory 14. As described above, “D×D×D” addresses areprepared in the LUT memory 14 and RGB data (hereinafter, referred to as“K data”) after color conversion is stored in each of the addresses.That is, assuming that the address space of the LUT memory 14 is athree-dimensional space having an R axis, a G axis, and a B axis asshown in FIG. 3, it may be thought that this space is divided into“D×D×D” (D=5 in the case shown in FIG. 3) cubic regions and K datacorresponds to a lattice point of each cubic region.

When there is an access including designation of an address from theaddress operation circuit 12, the LUT memory 14 outputs K datacorresponding to the address to the interpolation operation circuit 16to be described later. At this time, in addition to the K data, the LUTmemory 14 outputs three kinds of RGB data, which is adjacent to the Kdata in a three-dimensional space, to the interpolation operationcircuit 16. The data is called “W data”, “S data”, and “T data”,respectively. Such data is supplied for interpolation processing of Kdata in the interpolation operation circuit 16. Details of theinterpolation processing will be described later.

The address operation circuit 12 calculates an address accessing the LUTmemory 14 on the basis of RGB data (hereinafter, referred to as“original RGB data”) input from the input interface 170. Specifically,high-order U-bit data is taken out as a first portion from original RGBdata for every R, G, and B, and an address for accessing the LUT memory14 is obtained by using the U-bit data taken out as described above. Theaddress obtained herein specifies one cubic region among the “D×D×D”cubic regions shown in FIG. 3.

The address operation circuit 12 varies the bit number “U” according toa mode signal input from the control unit 40. Specifically, when themode signal indicates a cinema mode, the address operation circuit 12sets the bit number “U” to “4”. In addition, when the mode signalindicates a television mode, the bit number “U” is set to “3”. Inaddition, when the mode signal indicates a presentation mode, the bitnumber “U” is set to “2”. That is, the address operation circuit 12takes out data corresponding to a bit number, which is needed when avalue obtained by deducting “1” from a color depth D of an image outputmode set by a user is expressed as a binary number, from high-order bitsof the original RGB data. The relationship between the color depth D andthe bit number U is expressed as an expression of “D=2^U+1”. Here, “^”is a symbol indicating the power.

FIG. 4 is an explanatory view illustrating a method of calculating anaddress when a cinema mode is set. Since the bit number “U” is “4” whensetting the cinema mode, the address operation circuit 12 takes outhigh-order 4-bit data from the original RGB data for every R, G, and B.Then, the original RGB data with 256 steps of each color is convertedinto a value with 16 steps (0 to 15) of each color by the 4-bit data.The address operation circuit 12 makes addresses of the 3D-LUTcorrespond to all combinations of the 4-bit data in advance. In thismanner, the address operation circuit 12 can easily acquire addresses ofthe 3D-LUT when setting the cinema mode. However, in the case when anyone of the original R, G, and B data is “255”, an address that cannot beacquired only by high-order 4-bit data is prepared specially in order tosuppress an error of an interpolation operation performed by theinterpolation operation circuit 16, which will be described later. Amongaddresses shown in FIG. 4, those corresponding to the special addressesare addresses “17”, “288”, and “4912”. That is, in the case when a valueof any one of R, G, and B among the original RGB data is “255”, theaddress operation circuit 12 calculates the special addresscorresponding to the combination of R, G, and B having the value. Inother cases, the address operation circuit 12 calculates an addressusing high-order 4-bit data.

FIG. 5 is an explanatory view illustrating a method of calculating anaddress when a television mode is set. In addition, FIG. 6 is anexplanatory view illustrating a method of calculating an address when apresentation mode is set. Even in these modes, it is possible tocalculate addresses of the LUT memory 14 by taking out high-order U-bitdata from original RGB data in the same method as when the cinema modeis set.

Furthermore, the address operation circuit 12 takes out low-order L-bit(L=8−U) data as a second portion from original RGB data for every R, G,and B and then outputs the data to the interpolation operation circuit16. Specifically, when the cinema mode is set, the address operationcircuit 12 takes out low-order O-bit data of the original RGB data forevery R, G, and B and then outputs the data to the interpolationoperation circuit 16. Similarly, low-order 5-bit data is output to theinterpolation operation circuit 16 when the television mode is set, andlow-order 6-bit data is output to the interpolation operation circuit 16when the presentation mode is set. Such data is used as parameters forinterpolating K data output from the LUT memory 14 in the interpolationoperation circuit 16. Thus, in the present embodiment, data of allportions excluding high-order U bits is used as parameters for theinterpolation operation. However, a specific portion of low-order bitsexcluding the high-order U bits may also be used as a parameter for theinterpolation operation. In the following description, it is assumedthat low-order L-bit data of R data is “xf data”, low-order L-bit dataof G data is “yf data”, and low-order L-bit data of B data is “zf data”.

The address operation circuit 12 performs processing for selecting onetetrahedron from six tetrahedrons included in one cubic region, which isspecified by high-order U-bit data of the original RGB data, on thebasis of the size relationship among xf data, yf data, and zf data. Whenthe one tetrahedron is selected, the address operation circuit 12outputs an identification signal for identifying the selectedtetrahedron to the interpolation operation circuit 16. Here, the shapeof the selected tetrahedron determines the operation expression of aninterpolation operation performed by the interpolation operation circuit16.

FIG. 7 is an explanatory view illustrating types of six tetrahedronsincluded in one cubic region. As shown in the drawing, the sixtetrahedrons are obtained by dividing a cubic region using threesurfaces expressed by three kinds expressions of x=y, y=z, and z=x.Accordingly, regions possessed by six tetrahedrons T1 to T6 areexpressed by the following six conditional expressions. That is,expression (1), expression (2), expression (3), expression (4),expression (5), and expression (6) expresses the first tetrahedron T1,the second tetrahedron T2, the third tetrahedron T3, the fourthtetrahedron T4, the fifth tetrahedron T5, and the sixth tetrahedron T6,respectively.x≧z≧y  (1)x≧y>z  (2)y>x≧z  (3)y>z>x  (4)z≧y>x  (5)z>x≧y  (6)

FIG. 8 is an explanatory view conceptually illustrating how atetrahedron is selected by the address operation circuit 12. As shown inthe drawing, assuming that a coordinate within a cubic region determinedby xf data, yf data, and zf data is A(xf, yf, zf), the address operationcircuit 12 can determine in which tetrahedron the coordinate A exists bychecking which one of the expressions (1) to (6) is satisfied by thecoordinate. In the example shown in FIG. 8, since the coordinate Asatisfies a condition of the expression (2), the second tetrahedron T2is selected by the address operation circuit 12.

After the tetrahedron is selected as described above, the addressoperation circuit 12 determines “W data”, “S data”, and “T data”, whichare output to the interpolation operation circuit 16, on the basis ofthe shape of the tetrahedron as follows.

An origin of the xyz coordinate shown in FIG. 8 corresponds to a latticepoint (hereinafter, referred to as a “K point”) at which the “K data” islocated. Here, a point farthest from the K point among eight apices ofthe cubic region shown in FIG. 8 is set to a W point. The W point is apoint of expressing a color closest to a white color in a cubic region.The address operation circuit 12 accesses an address of the LUT memory14 where the W point exists. Then, the “W data” is output from the LUTmemory 14 to the interpolation operation circuit 16. The W point existsat the same position as a “K point” of a cube that is adjacent to a sideof the cube, which is shown in FIG. 8, in the front upper rightdirection thereof. Therefore, “K data” stored in the address is outputas “W data” to the interpolation operation circuit 16 by accessing anaddress corresponding to the K point of the cube adjacent thereto.

In the present embodiment, of two points other than the K point and theW point that form the second tetrahedron T2, one point close to the Kpoint is set as an S point and the remaining one point is set as a Tpoint. The address operation circuit 12 accesses an address of the LUTmemory 14 where the S point and the T point exist. Then, the “S data”and the “T data” are output from the LUT memory 14 to the interpolationoperation circuit 16. That is, “K data” corresponding to a K point of atetrahedron that is adjacent to a front side of the cube shown in FIG. 8is output as “S data”, and “K data” corresponding to a K point of atetrahedron that is adjacent to an inclined front side of the cube shownin FIG. 8 is output as “T data”. Moreover, in the present embodiment,regardless of which tetrahedron is selected by the address operationcircuit 12, a point, which is close to the K point, of two points otherthan the K point and the W point is set as an S point and the remainingone point is set as a T point.

The interpolation operation circuit 16 is input with “K data” outputfrom the LUT memory 14 and performs processing for interpolating the “Kdata” to the 256-step color depth. That is, the interpolation operationcircuit 16 performs processing for interpolating RGB data, of which acolor depth has been reduced up to 17 steps in the cinema mode, 9 stepsin the television mode, and 5 steps in the presentation mode, up to 256steps that are the same color depth as original RGB data.

To the interpolation operation circuit 16, the xf data, the yf data, andthe zf data are input from the address operation circuit 12 and a signalfor identifying the selected tetrahedron is input. In addition, the Kdata, the W data, the S data, and the T data are input from the LUTmemory 14 to the interpolation operation circuit 16. In addition, theinterpolation operation circuit 16 performs an operation ofinterpolating the K data using those data. When the K data afterinterpolation is expressed as “KK”, the “KK” can be calculated by thefollowing expression (7). The interpolation operation circuit 16 isconfigured to include an adder or subtracter, a multiplier, and adivider for realizing the expression (7). The interpolation operationcircuit 16 can output RGB data having a 256-step color depth byperforming the calculation for all of the R data, the G data, and the Bdata included in the K data. A method of the interpolation operationusing a tetrahedron is disclosed in detail in JP-B-58-16180. By adoptingthe following expression (7), it becomes possible to reduce the numberof multipliers compared with a case of adopting the expression disclosedin JP-B-58-16180. As a result, the circuit size of the interpolationoperation circuit 16 can be made small.KK=K+(W−K)·h/E−(W−T)·(h−n)/E−(T−S)·(h−m)/E  (7)

In addition, the interpolation operation circuit substitutes xf data, yfdata, and zf data for parameters “h”, “m”, and “n” of the aboveexpression according to the type of a tetrahedron indicated by anidentification signal input from the address operation circuit 12.Specifically, the substitution is performed according to the followingconditions.

(a) First tetrahedron T1: h=xf, m=zf, and n=yf

(b) Second tetrahedron T2: h=xf, m=yf, and n=zf

(c) Third tetrahedron T3: h=yf, m=xf, and n=zf

(d) Fourth tetrahedron T4: h=yf, m=zf, and n=xf

(e) Fifth tetrahedron T5: h=zf, m=yf, and n=xf

(f) Sixth tetrahedron T6: h=zf, m=xf, and n=yf

Furthermore, the parameter “E” of the above expression (7) indicates thelength of one side of the cubic region shown in FIG. 8. A value of theparameter depends on the color depth at the time of color conversion ineach image output mode. That is, in the case of a cinema mode, the valueof E is set to “16” since RGB data has a discrete value every 16 values,as shown in FIG. 4. Furthermore, in the case of a presentation mode, thevalue of E is set to “64” since original RGB data has a discrete valueevery 64 values, as shown in FIG. 6. The relationship is expressed as anexpression of “E=2^L”. The interpolation operation circuit 16 sets thevalue of E according to a mode signal input from the control unit 40.

In the projector 100 according to the present embodiment describedabove, when a user sets an image output mode through the operation panel180, the 3D-LUT corresponding to the image output mode is stored in theLUT memory 14. Furthermore, in the address operation circuit 12,calculation of an address corresponding to the image output mode isperformed. Furthermore, in the interpolation operation circuit 16, aparameter substituted for the above expression (7) corresponding to theimage output mode is changed. Therefore, in the projector 100 accordingto the present embodiment, color conversion corresponding to variouskinds of precision can be performed with one kind of image processingcircuit 110.

Furthermore, in the present embodiment, the precision of colorconversion is made to change according to an image output mode set by auser. In contrast, the precision of color conversion may be fixed forevery model of the projector 100, for example, such that a projector formovie fans has a 17-step color depth or a projector in a low price rangehas a 9-step color depth. The image processing circuit 110 provided inthe projector 100 according to the present embodiment can perform colorconversion with various kinds of precision as described above.Therefore, the image processing circuit 110 in the present embodimentcan be mounted in common in different kinds of projectors. As a result,since a member can be shared, it becomes possible to reduce amanufacturing cost. In this case, designation of an image output mode tothe address operation circuit 12 and the interpolation operation circuit16 is not designation made by the control unit 40 but may be performedby a DIP switch, a jumper pin, or a fixed circuit.

C. MODIFICATIONS

While various embodiments of the invention have been described, theinvention is not limited to such embodiments but various modificationsmay be made within the scope without departing from the subject matteror spirit of the invention. For example, a function realized by hardwaremay be realized by software. In addition, the following modificationsmay also be made.

C1. First Modification

In the embodiment described above, a special address of the 3D-LUT iscalculated in the case where original RGB data is “255”. However, thespecial address may not be prepared. In this case, the address operationcircuit 12 can perform calculation of an address with only high-orderU-bit data. In this case, the relationship between the color depth Dafter color conversion and the bit number U of high-order bits is D=2^U.

C2. Second Modification

In the embodiment described above, the above expression (7) is adoptedas an expression for performing an interpolation operation. However, thefollowing expressions (8) and (9) which are expressions equivalent tothe expression (7) may also be adopted.KK=K·(1−h/E)+S·((h−m)/E)+T((m−n)/E)+W·n/E  (8)KK=K+(S−K)·h/E+(T−S)·m/E+(W−T)·n/E  (9)

C3. Third Modification

In the embodiment described above, the liquid crystal panel 140 is usedas a light valve that modulates light emitted from the light sourceportion 150. However, elements, such as a DMD (digital micromirrordevice) and an LCOS (liquid crystal on silicon), may also be used aslight valves. In addition, an image may also be projected on a screenusing CRT. In addition, the “DMD” is a trademark of Texas Instrument,Inc., USA.

C4. Fourth Modification

In the embodiment described above, the image processing circuit 110shown in FIG. 2 is mounted in the projector 100. However, the imageprocessing circuit 110 may also be mounted in monitor direct view typedisplay devices, such as a liquid crystal display, a plasma display, anda CRT display. In addition, the image processing circuit 110 may also bemounted in image output devices, such as a DVD player, a DVD recorder, avideo cassette recorder, and a personal computer. In addition, theprojector 100 may be a front projector or a rear projector.

1. An image processing device for color conversion, the image processing device comprising: an input unit to which an image signal expressing an image is input; a selection unit for selecting an image output mode, the image output mode having at least three different preset display modes that are displayed without regard to the image signal that is input into the input unit; a memory that stores three-dimensional lookup table (3D-LUT) data, which is determined according to the selected image output mode, the amount of the 3D-LUT data in the memory varies according to the selected image output mode; an interpolation unit that interpolates the image signal on the basis of the 3D-LUT data stored in the memory; and an address specifying unit that is configured to divide the image signal into high-order bit data and low-order bit data on a boundary determined according to a color depth, wherein the memory that stores 3D-LUT data outputs at least three different types of image signals.
 2. The image processing device according to claim 1, wherein a precision of color conversion differs according to the selected image output mode.
 3. The image processing device according to claim 1, wherein the output mode includes at least one of a first mode suitable for movie, a second mode suitable for television program, and a third mode suitable for presentation.
 4. The image processing device according to claim 1, further comprising: a color converting unit that converts the image signal into the 3D-LUT data by referring to the memory on the basis of a first portion of the image signal, wherein the interpolation unit interpolates the image signal on the basis of the 3D-LUT data and a parameter which is specified on the basis of a second portion other than the first portion of the image signal.
 5. The image processing device according to claim 4, wherein the first portion of the image signal is high-order bit data of the image signal.
 6. The image processing device according to claim 4, wherein the second portion of the image signal is low-order bit data of the image signal.
 7. An image display device comprising: the image processing device according to claim 1; and a display unit that displays the image based on the image signal.
 8. The image display device according to claim 7 configured as a projector.
 9. A method for displaying an image by an image display device, the method comprising: inputting an image signal expressing the image to the image display device; selecting a image output mode of the image display device from a selection unit, the image output mode having at least three different preset display modes; storing three-dimensional lookup table (3D-LUT) data, which is determined according to the selected image output mode, in a memory included in the image display device; varying the amount of the 3D-LUT data in the memory according to the selected image output mode; dividing the image signal into high-order bit data and low-order bit data on a boundary determined according to a color depth; outputting at least three different types of image signals from the memory included in the image display device; interpolating the image signal on the basis of the 3D-LUT data stored in the memory; and displaying the image based on the image signal. 